Rock stabilizing apparatus

ABSTRACT

Rock stabilizing apparatus having a tension member adapted to be inserted in a drill hole and being adapted to be cemented at an inner end to the drill hole walls. A longitudinally segmented expansion member having a tapered bore and a radially extending flange fits over the tension member and is insertable in the hole. A tapered wedge slidable of the tension member is forced into the tapered bore of the expanding member by operation of a nut threaded on an outer end of the tension member so that the expansion member expands outwards against the drill hole walls, and at the same time, the flange is pressed against the rock face so as to develop lateral compressive stresses in the rock adjacent the rock face and longitudinal compressive stresses in the rock longitudinally of the tension member.

United States Patent Karara [4 1 Sept. 26, 1972 ROCK STABILIZING APPARATUS 1,173,054 7/1964 Germany ..61/45 B [72] Inventor: Said M. Karara, Stewart, British Columbia, Canada Pnmary Exammer-Denn1s L. Taylor Attorney-Brian J. Wood [22] Filed: Jan. 25, 1971 21 Appl. No.: 109,161 [57] ABSTRACT Rock stabilizing apparatus having a tension member 52 US. Cl. ..61/45 B adapted be inserted in a drill and being [51] Int. Cl. ..E21d 21/00 adapted to be cemented at an inner end to the drm 581 Field of Search ..61/45 B; 85/86, 87, 88, 68, Walls- A mg'tudmany Segmented expansm 85/67. 52/698 704 705 707 member having a tapered bore and a radially extending flange fits over the tension member and is inserta- [56] References Cited ble in the hole. A tapered wedge slidable of the ten- 1 sion member is forced into the tapered bore of the ex- UNITED STATES PATENTS panding member by operation of a nut threaded on an v l 296 374 3/1919 Droe e et al 85,87 outer end of the tension member so that the expansion 1 0/19 50 Ben g B X member expands outwards against the drill hole walls, l038834 9/19 B1010 85/67 and at the same time, the flange is pressed against the l429298 9/1922 Pleister' /67 X rock face so as to develop lateral compressive stresses l469665 10/1923 g 85/67 in the rock adjacent the rock face and longitudinal compressive stresses in the rock longitudinally of the FOREIGN PATENTS OR APPLICATIONS tension member- I 933,324 9/ 1955 Germany ..6l/45 B 1 Claim, 3 Drawing Figures PAIENTEnsms m2 SHEET 1 0F 2 Said M. Karara PATENTEDSEPZBIBYZ 3.693.359

SHEET E'UF 2 I Said M. Karara,

Inventor Lyle G. orey,

Agel

1 ROCK sTABILIzINc APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for stabilizing rock faces in general, and in particular face rock of mine roofs.

2. Prior Art In the use of rock as a structural material two major problems are involved in design. Engineering properties of the rock are not well known not easily measured, and action of artificial support'for rock structures is not well understood. 7

TA. Lang in his Theory and Practice of Rock Bolting, L.A. Panek in his Principles of Reinforcing Bedded Mine Roofs withBolts and E. Parsons in his Design and Development of a Rock Bolt Anchored by Explosive Forming have postulated possible effects of rock bolting in various kinds of rock members such as laminated beams and circular openings. Although rock bolts are extensively used in mines, rock tunnels, etc. design is empirical in nature. Also knowledge of force fields applied to rock by rock bolt assemblies is limited.

It has long been considered, and now generally accepted, that stress distribution in rock forming a mine roof is much the same as stress distribution in a uniformly loaded beam fixed and supported at its ends. In beams, as well known, compressive stresses are developed above a neutral axis, maximum in upper fibers of the beam and tension stresses are developed below the neutral axis maximum in lower fibers of the beam. 1

correspondingly, in mine roof rock a face zone, depth of which is dependent on roof span and the physical characteristics of the rock, is subJected to tensile stresses, rock above that face zone being under compression. Rock in the face zone is, consequently, subject to fracture propagation and eventual failure, due to inherent weakness of rock under tension.

Standard rock bolts now in use generally have a bolt, which is anchored at its inner end to walls of the drill hole, the drill hole being extended from the rock face inwards to sound rock, i.e. rock under compression,

and a bearing plate fitted over the bolt and tightened against the rock face by a nut threaded on the bolt. High tensile stresses are developed in the bolt and corresponding longitudinal compressive stresses are developed in the bolted rock resulting in an increase in shear strength of therock and an effective build-up of a monolithic rock mass.

Standard rock bolts, however, do little to relieve and in fact add to, the flexural tensile stress in the face zone and unless rock bolts are spaced at close intervals fractured face rock between bolts can fail.

SUMMARY OF THE INVENTION The present invention provides apparatus for stabilizing a rock mass particularly rock forming a mine roof to reduce and effectively cancel tensile stresses in the face zone and, consequently, reduce likelihood of fracture propagation and roof failure.

The present invention also develops compressive stresses in a direction normal to the face of the mine tional design, build up a monolithic rock mass.

The apparatus of the present invention includes a tension memberadapted to be fitted in a drill hole in rock mass, the tension member having an inner end adapted to be cemented to the walls of the drill hole, a longitudinally segmented expansion member having a radial flange at one end and having a tapered bore slidably mounted on the tension member for insertion in the drill hole, a tapered wedge slidably mounted on the tension member for movement into the tapered bore, and a nut threaded on an outer end of the tension member operable for forcing the wedge into the tapered bore so as to expand the expansion member and force it against walls of the drill hole and at the same time to force the flange against the face of the rock mass so as to develop lateral compressive stresses in the rock adjacent the rock face and longitudinal compressive stresses in the rock longitudinally of the tension member. I

A detail description following, related to drawings, gives exemplification of apparatus according to the invention, which, however, is capable of expression in means other than those particularly described and illustrated.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section of stabilizing apparatus of the invention applied to a mine roof,

FIG. 2 is a section on 2-2 of FIG. 1,

FIG. 3 shows, diagrammatically, application of the I rock stabilizing apparatus in a mine roof and associated stress distribution.

DETAILED DESCRIPTION FIGS. 1 and 2 I FIG. 1 shows one embodiment of rock stabilizing apparatus, generally 10, installed in a drill hole 11 of a mine roof 12 having a face 12.1. The apparatus 10 includes a tension member 13, an expandable member 14 which fits over the tension member and is insertable in the drill hole, a wedge 15 slidable of the tension member into and out of wedging engagement with the expandable member and a nut 17 threaded on the tension member for forcing the wedge into wedging engagement so as to spread the expandable member radially against walls of the drill hole.

The tension member 13 is a long bolt roughened by corrugations adjacent an inner end 18. Length of the bolt is such that when the inner end 18 is positioned at or near a bottom 19 of the hole a threaded outer end portion 21 extends outwards of the face 12.1 of the mine roof.

The expandable member 14 FIG. 1 and 2, has a cylindrical sleeve 23 having a tapered axial bore 24 which tapers from one end 25 of the sleeve to an opposite end 26. The sleeve has a square flange at its end 25, the flange having an opening 28 registering with the axial bore 24. The sleeve, outer diameter of which enables it to be inserted in the drill hole is longitudinally segmented, FIG. 2, and the flange 27, is out along severance lines 29 to permit radial expansion of the sleeve. Minimum diameter of the tapered bore of the sleeve is greater than bolt diameter so as to enable the sleeve to be fitted over and move longitudinally of the bolt.

FIGS. 1 and 3 The wedge is frusto-conical having a cylindrical axial bore 31 diameter of which is a little greater than the bolt diameter so as to provide a slidable fit of the wedge on the bolt. Taper angle of the wedge corresponds to the taper angle of the tapered bore and the wedge is such that with the wedge fitted in the tapered bore a butt end portion 33, FIG. 1, of the wedge, projects'outwards of the flange 27, approximately 1% inch to 1 inch.

OPERATION Referring to FIG. 3, due to lack of support tensile stresses, arrows 35, are developed in a face zone 36 of the mine roof l2, depth D of the face zone generally being a function of the unsupported span S of the mine roof and physical characteristics of the rock mass. Rock above the face zone 36 is usually under compression. Cracks 38, therefore, can propagate in the face zone resulting in dangerous, and sometimes fatal, rock falls.

In applying the rock stabilizing apparatus 10, a pair being shown in FIG..3, drill holes 11 are extended from the face 12.1 through the face zone 36 and well into rock under compression. Tension members having a length in excess of depth of the drill holes are selected and anchored at their inner ends by an epoxy cement 37, see FIGS. 1 and 3. Use of epoxy cement for this purpose is well known and need not be described. The tension members are positioned longitudinally of the drill holes with their threaded outer end portions 21 extending clear of the face 12.1.

After the epoxy cement has hardened sufficiently an expandable member 14 is fitted over each tension member and the sleeve 23 of each expandable member inserted as far as it will go in a drill hole, that is until the flanges 27 engage the face 12.1 of the rock. A wedge 15, a washer 39 and the nut 17 are then fitted to each of the tension members, the nuts being tightened against sive stresses through pressure of the flange against the rock face 12.1, arrows 43, in a direction generally longitudinally of the drill'holes. At the same time expan- -sion of the sleeve against the drill hole walls develops lateral compressive stresses, arrows 41, in, and thus stabilize, the face zone. Magnitude of compressive stresses in both directions is a function of spacing, tension applied to the tensionmembers and the taper angle of the wedges. The rock in the face zone can, accordingly, be compressively stressed sufficiently to cancel flexural tensile stresses so that the roof, in fact, acts as a prestressed beam. As the lateral compressive stresses exerted by the expansion sleeve into the intimate part of the rock, the first 6 inches of rock around the hole in this area are very high and there is the possibility that the rock in this area might fail under shear, the flange fixed to the end of the sleeve exerts longitudinal compressive stresses which reduces shear stress due to the lateral stresses and consequently restores the rock around the hole in a condition suitable for conveying the lateral stresses to the adjacent rock mass.

Iclaim: 1. Rock stabilizing apparatus for stabilizing a rock mass having a drill hole opening out of a rock face, the

apparatus including:

a. a tension member adapted to be inserted in the drill hole, the tension member having an inner end portion adapted to be cemented in the drill hole and having a threaded outer end,

b. a longitudinally segmented cylindrical expansion member having a tapered bore slidably mounted on the tension member for insertion into the drill hole,

c. a radially segmented flange at the outer end of the expansion member engagable with the rock face,

. a tapered wedge slidably mounted on the tension member,

e. a nut threaded on the threaded end of the tension member operable for forcing the wedge into the bore of the expansion member so as to spread the expansion member against the walls of the drill hole and press the flange against the rock face. 

1. Rock stabilizing apparatus for stabilizing a rock mass having a drill hole opening out of a rock face, the apparatus including: a. a tension member adapted to be inserted in the drill hole, the tension member having an inner end portion adapted to be cemented in the drill hole and having a threaded outer end, b. a longitudinally segmented cylindrical expansion member having a tapered bore slidably mounted on the tension member for insertion into the drill hole, c. a radially segmented flange at the outer end of the expansion member engagable with the rock face, d. a tapered wedge slidably mounted on the tension member, e. a nut threaded on the threaded end of the tension member operable for forcing the wedge into the bore of the expansion member so as to spread the expansion member against the walls of the drill hole and press the flange against the rock face. 